Photographic materials and method of producing the same



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This invention relates to photographic materials and to methods of preparing them. More particularly, this invention relates to light-sensitive silver halide emulsions containing polyvinylpyrrolidone-halogen as a stabilizing and antifogging agent, to methods of producing the emulsions and coating them on a base, and to the so-coated base.

It is well known in the photographic art that 1ight sensitive emulsions, such as gelatino-silver halide emulsions, have a tendency to fog. Fog is usually caused by a prolonged ripening of the emulsions, by prolonged storage especially at elevated temperatures and humidity, and by prolonged development. To overcome this undesirable property, it has been the practice in this art to add certain chemical compounds to the emulsions to increase their stability and to reduce their tendency to fog. However, all stabilizing and antifogging compounds heretofore used in this art have the disadvantage that upon addition to the emulsion they cause a loss of speed and/or contrast of the emulsion.

It is, accordingly, an object of this invention to produce a light-sensitive emulsion which is fast, stable, has a reduced tendency to fog and has good contrast.

A further object of this invention resides in a lightsensitive emulsion which contains a compound which stabilizes the emulsion against fogging and at the same time does not materially reduce the speed and/or the contrast of the emulsion.

A still further object of this invention is to provide a light-sensitive emulsion containing therein polyvinyl-pyrrolidone-halogen as an antifogging and stabilizing agent.

We have discovered that a polyvinylpyrrolidone-halogen such as polyvinylpyrrolidone-idine (see U.S.P. 2,- 739,922) or polyvinylpyrrolidone containing chlorine or bromine and iodine (see U.S.P. 2,754,245) when added to a light-sensitive silver halide emulsion, stabilizes and inhibits the fogging of the emulsion. The reduction of the tendency of the emulsion to fog is very pronounced after it has been submitted to an incubation test. In the incubation test, the photographic film or paper, after being coated with the emulsion, is held for a predetermined time at elevated temperature and at high humidity. When the antifogging agent of our invention is added to the emulsion, no loss of speed is caused by the incubation test. Sometimes, when very high concentrations of the antifogging agent of our invention are used, there will be some loss of speed when the emulsion is tested immediately after coating it on the film or paper. However, after incubation, the emulsion regains its original speed but retains its reduced tendency to fog.

The antifogging agent of our invention may be added to the emulsion at any stage during its process of production. Thus, it may be added as a ripening fina or as a coating final. When added as a ripening final, it is added during the ripening or sensitivity increasing stage of the emulsion making process. Such addition may be made before, during or after the addition of the soluble silver salt to the soluble halide in the presence of a suitable colloid, such as gelatin, polyvinyl alcohol, solubilized case- States Parent 0 3,021,213 Patented Feb. 13, 1962 ice in or albumin. When added as a coating final, the antifogging agent of our invention is added to the emulsion just prior to coating it on a suitable support such as glass, paper or film at a time when the emulsion has nearly attained its maximum sensitivity.

In some instances, it is advantageous to apply the anti fogging and stabilizing compound of our invention in a separate layer such as an undercoating layer or in an antiabrasio'n gelatin surface. Sometimes it is desirable to incorporate the compound in one or all processing baths or in the pre-- and post-baths.-

When used as a ripening final, the polyvinylpyr rolidone halo'gen is preferably added to the emulsion in an amount ranging from 1 milligram to milligrams per 0.4 mol of silver halide and when used as a coating final" it is preferably added in an amount ranging from 10 milligrams to 1 gram per 0.4 mol of silver halide. The optimum amount to be added depends primarily on the type of emulsion and should be determined individually in each case.

The polyvinylpyrrolidone-halogen of our invention may also be used in combination with known antifoggants and stabilizers. The antifoggant of our invention can also be used in combination with sensitizers such as sulfur, metal and reduction sensitizers as' well as with accelerators such as the polyoxyethylenes (see U.S.P. 1,970,578) and their derivatives and polyvinylpyrrolidone.

The novel antifoggant of our invention may be used with various types of photographic emulsions, such as nonsensitized orthochromatic, panchromatic and X-ray emulsions, paper emulsions and color emulsions.

The polyvinylpyrrolidone-halogen we prefer to use as an antifoggant is polyvinylpyrrolidone-iodine. This is a known compound, and while its chemical structure has not been definitely established, it is known to contain a substantial quantity of iodine which is presumed to be bound to polyvinylpyrrolidone in a manner similar to the manner in which iodine is bound to starch. The halogen concentration may range from 2 to 35%.

The following example is given of the manner in which the antifoggant of our invention can be used. It is to be understood, however, that this example is given by Way of illustration and not by way of limitation.

Example A silver halide emulsion in gelatin was prepared in a conventional manner and brought up to its maximum light sensitivity. The silver halide used to form the emulsion consisted of 4% silver iodide and 96% silver bromide. The emulsion was then readied for coating, and finals, such as sensitizing dyes, stabilizers and hardening agents were added. A 1% solution of polyvinylpyrrolidone-iodine in water was prepared and added in varying amounts to samples of the emulsion as an antifoggant and stabilizer. Each sample contained about .4 mol of silver halide. The so-prepared emulsion samples were each coated on a suitable cellulose ester base and dried. These coated film samples were then exposed in a Type IIB Sensitometer and developed in a developer of the following composition:

Water to make 1.0 liter.

The results obtained were as follows:

Our invention is not limited to the detailed description contained herein, but includes all modifications that fall within the scope of the appended claims.

We claim:

1. A ripened light-sensitive emulsion comprising a silver halide dispersed in a photographic colloid to which has been added, after formation of the silver halide, from 1 to 300 milligrams of polyvinylpyrrolidone-halogen per .4 mol of silver halide as an antifogging and stabilizing agent.

2. A ripened light-sensitive gelatiuo-silver halide emulsion to which has been added, after formation of the silver halide, from 1 to 300 milligrams of polyvinylpyrrolidoneiodine per .4 mol of silver halide as an antifogging and stabilizing agent.

3. A ripened light-sensitive gelatino-silver halide emulsion to which has been added, after formation of the silver halide, from to 300 milligrams of polyvinylpyrrolidone iodine per .4 mol of silver halide as an antifogging and stabilizing agent.

4. A ripened light-sensitive gelatino-silver halide emulsion as recited in claim 2 containing an optical sensitizer.

5. A ripened light-sensitive geIatino-silver halide emulsion as recited in claim 2 containing an accelerator.

6. A light-sensitive photographic element comprising a base and a coating of gelatino-silver halide emulsion thereon to which emulsion has been added, after formation of the silver halide, 1 to 300 milligrams of a polyvinylpyrrolidone-halogen as an antifogging and stabilizing agent.

7. A light-sensitive photographic element as recited in claim 6 wherein the polyvinylpyrrolidone-halogen is polyvinylpyrrolidone-iodine.

8. A light-sensitive element comprising a base, a layer of a silver halide emulsion thereon, and a separate layer containing polyvinylpyrrolidone-iodine adjacent said firstmentioned layer, said last-mentioned layer serving as an antifogging and stabilizing compound for said emulsion.

9. A process of forming a photographic emulsion having a reduced tendency to fog which comprises producing an emulsion by first forming a dispersion of silver halide in a photographic colloid and thereafter ripening the emulsion and during said ripening adding a polyvinylpyrrolidone-halogen thereto.

10. A process of forming a photographic emulsion as recited in claim 9 wherein the polyvinylpyrrolidonehalogen is polyvinylpyrrolidone-iodine.

11. A process of forming a light-sensitive photographic element having a reduced tendency to fog which comprises forming a gelatino-silver halide emulsion, ripening said emulsion, coating said emulsion on a base and add ing polyvinylpyrrolidone-iodine to said emulsion just prior to the coating thereof on said base.

References Cited in the file of this patent UNITED STATES PATENTS Hosmer July 10, 1956 

8. A LIGHT-SENSITIVE ELEMENT COMPRISING A BASE, A LAYER OF A SILVER HALIDE EMULSION THEREON, AND A SEPARATE LAYER CONTAINING POLYVINYLPYRROLIDONE-IODINE ADJACENT SAID FIRST MENTIONED LAYER, SAID LAST-MENTIONE D LAYER SERVING AS AN ANTIFOGGING AND STABILIZING COMPOUND FOR SAID EMULSION. 